Author Topic: Long Exposure ETTR setting  (Read 8261 times)

garry23

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Long Exposure ETTR setting
« on: July 29, 2014, 12:45:57 AM »
As someone who uses high NDs, eg 4, 10 and thus 14, for LE photography, the challenge is ‘guessing’ the exposure, especially at the 10 or 14 level.
I have been experimenting with A-ETTR and believe I am close to this being a LE photographers’ savior. But the current coding of ETTR does not always find a solution.

My first ‘non-optimal’ ML-enhanced workflow goes like this:
•   Compose & focus without the filters on;
•   Place the filters on the camera;
•   Set the ISO;
•   Set the shutter speed to anything between 1 and 30 seconds, according the scene;
•   Set an aperture, eg F/22 or F/16 or something;
•   Press ETTR and get ML to adjust the ISO (normally ETTR always prefers low ISO solutions), ie don’t touch the exposure time or aperture, ‘just’ seek a solution for ISO;
•   Adjust the shutter time and F-number if ETTR fails to get a solution;
•   Take note of the ISO and adjust it down to 100 and change the shutter speed and/or aperture accordingly.

My ideal ML-enhanced LE workflow is as follows (but it needs coding, which I can’t do):
•   Compose & focus without the filters on;
•   Set the aperture for the desired ‘look’;
•   Set the ISO;
•   Place the filters on the camera;
•   Set ‘LE solution’ in the A-ETTR menu, ie a new setting yet to be coded;
•   Press ETTR to get an LE solution, ie the required LE shutter time (or a pretty good guess) at the F number and ISO you set, irrespective of the time or the ND filters you have put on the camera (ideally this time would be passed to the ML bulb timer, ie a perfect world).

Are there any other LE photographers out there looking for an ML ‘LE ND filter’ helper? Do the coders think this feature worthy of including in the ‘things to do’ list?


brapodam

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Re: Long Exposure ETTR setting
« Reply #1 on: July 29, 2014, 01:36:26 AM »
I do long exposures quite frequently, but mostly during sunrise/sunset. This is a cool idea, but I see 2 potential problems

1. During sunrise/sunset times, the light conditions change too fast. By the time you screw on the ND filter, your exposure needs to change. I normally just ETTR before I put on the ND, then use a phone app to get the required shutter speed, and compensate for the change in light.
2. People who use a ND filter usually want a specific exposure time, not an automatic solution. I might want 30s to smooth out clouds, or 2s to have a nice wave formation. This is why I usually make sure that my exposure time before the ND filter is a specific one, then I'll compensate for the ND only with shutter speed (and ISO if required)

garry23

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Re: Long Exposure ETTR setting
« Reply #2 on: July 29, 2014, 01:58:19 AM »
@brapodam

I understand fully what you are saying.

I'm suggesting that with ETTR we have another workflow.

Taking an ETTR reading is seconds.

To be clear, my ideal workflow would be as follows (based on having a fixed ND 'stack':
1. Compose & focus, of course;
2. Put on the filter(s) you have - for most of us having one or two is a luxury, ie we don't normally use the ND as a 'variable' in LE shooting (no pun intended wrt variable NDs);
3. Set ISO 100 and a mid aperture and get ML to estimate the LE shutter speed;
4. Adjust aperture and ISO to get a shuuter speed nearer to your artist desire, assuming you weren't lucky first time.

As I say, if ETTR could be enhanced to give us a shutter speed, for a given ISO and aperture, I believe it will greatly help with LE, as you wony need any apps!

brapodam

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Re: Long Exposure ETTR setting
« Reply #3 on: July 29, 2014, 02:50:01 AM »
@brapodam

I understand fully what you are saying.

I'm suggesting that with ETTR we have another workflow.

Taking an ETTR reading is seconds.

To be clear, my ideal workflow would be as follows (based on having a fixed ND 'stack':
1. Compose & focus, of course;
2. Put on the filter(s) you have - for most of us having one or two is a luxury, ie we don't normally use the ND as a 'variable' in LE shooting (no pun intended wrt variable NDs);
3. Set ISO 100 and a mid aperture and get ML to estimate the LE shutter speed;
4. Adjust aperture and ISO to get a shuuter speed nearer to your artist desire, assuming you weren't lucky first time.

As I say, if ETTR could be enhanced to give us a shutter speed, for a given ISO and aperture, I believe it will greatly help with LE, as you wony need any apps!
Hmm, perhaps a ND calculator integrated with ETTR? Workflow will be as follows:
1. Go into live view, compose, focus and press set to activate ETTR
2. Go into ML menu, set ND filter stops and target shutter speed (maybe even have an exposure offset function to compensate for changing light or the ND filter blocking off more light than specified)
2a. The ML menu shows you the ISO and aperture settings required for the target shutter speed (this is just a calculator based on the current exposure settings, no metering required)
3. Go back to live view, double press half shutter to set exposure settings, put on ND filter

As I have mentioned before, I usually want a specific shutter speed, so I want to lock that first before I care about aperture or ISO. I also try to use the lowest ISO, so unless I still don't have enough light when I have my lens wide open, I won't raise the ISO.

garry23

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Re: Long Exposure ETTR setting
« Reply #4 on: July 29, 2014, 03:20:31 AM »
The key thing is to ask a coder to tweak ETTR to provide exposures greater than 30(32) seconds.

Let's hope.

brapodam

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Re: Long Exposure ETTR setting
« Reply #5 on: July 29, 2014, 03:36:10 AM »
The key thing is to ask a coder to tweak ETTR to provide exposures greater than 30(32) seconds.

Let's hope.
Maybe have ETTR link to bulb timer, and we do everything in bulb mode? I don't think it's possible to set exposure >30s (32s) in manual mode. With ML bulb timer, bulb mode is pretty much manual mode without 30s limit anyway

EDIT: I see a problem with this: exp sim and histogram/zebras etc. when in bulb mode

garry23

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Re: Long Exposure ETTR setting
« Reply #6 on: July 29, 2014, 03:46:24 AM »
At the simplest level I would love ML ETTR to return any exposure as 'just' information, ie rather than a no solution message.

But as you say I preferably would like to see ETTR 'dump' the bulb exposure into the ML bulb setting.

I just hope someone tweaks ETTR with these LE ideas.

Such changes give ML additional functionality that simple can not be found elsewhere.

garry23

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Re: Long Exposure ETTR setting
« Reply #7 on: July 29, 2014, 03:18:40 PM »
@brapodam

Regarding your last edit.

This feature request is for when you have a fixed ND on your camera and you simply want to get the ETTR exposure time.

The user would select aperture and ISO and bulb-ETTR would set the exposure value in the ML bulb area OR a normal exposure if less than 30(32) seconds.

The user can then adjust aperture and ISO to adjust the exposure time for artist effect and undertake another ETTR if required, or use the first returned exposure and adjust that manually according to the aperture or ISO change.

I'm not looking for ML to automatically put you in bulb mode, but simply use the proposed bulb-ETTR setting to estimate the bulb time.  According to the exposure returned the user will use this seamlessly if less than 30(32) or switch to bulb and use ML bulb if greater than 30(32), ie ML returns an appropriate message, rather than just an error because the time us longer than 30(32).


dmilligan

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Re: Long Exposure ETTR setting
« Reply #8 on: July 29, 2014, 04:42:14 PM »
How about this:
  • You enter how many EVs your ND filter is in a menu
  • Take a picture (or just meter) in whatever mode using whatever metering you like (ETTR, manually adjust, or just Av, Tv or whatever) without the ND
  • ML detects when you switch to bulb mode and sets the bulb timer based on the current exposure settings and the ND stops setting
  • Attach the filter and take a pic
That would be really easy to code. You could also display on the screen what the bulb time would be for the current shutter speed setting and ND filter strength. That way if you want a specific time, you just do this in Tv or M, and set the shutter speed such that the computed shutter speed is what you want it to be.

garry23

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Re: Long Exposure ETTR setting
« Reply #9 on: July 29, 2014, 06:43:36 PM »
@dmilligan

I had thought of that, the real issue is when you are using high ND, ie over, say, ND4. If you are using an ND 10 or a stack to get ND14, say, you will find your exposure estimate based on simple ND math can be way out. Also NDs vary from manufacturer to manufacturer.

This is why I believe ML ETTR can help, ie get an ETTR-based exposure based on the actual ND in place.

If ETTR requires a boost in ISO to 'find' a solution, ie it's looking for pixel data, then the user can adjust accordingly when shooting.

As a first step, 'all' I'm looking for is for ETTR to provide exposure solutions greater than 30(32) for the ND in place, rather than provide an 'error' message as now.


dmilligan

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Re: Long Exposure ETTR setting
« Reply #10 on: July 29, 2014, 10:07:50 PM »
ND filters might be different from their spec, but once you accurately measure it, it should be consistent over time => you only need to measure it once. It would actually be pretty easy to have ML measure your ND filter too.

garry23

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Re: Long Exposure ETTR setting
« Reply #11 on: July 29, 2014, 10:20:44 PM »
Agree.

I would welcome seeing any ML approach to using ETTR and high density ND filters.

Fingers crossed ;-)

garry23

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Re: Long Exposure ETTR setting
« Reply #12 on: July 29, 2014, 11:52:36 PM »
@dmilligan
Thanks to your input above I have been experimenting with my ND1000 & ND16 on my 5DIII and my IR converted 50D. Here are my conclusions:

1.   Using in-camera ETTR hint in the RAW histobar gets me close to what I need, ie an in-camera estimate of the exposure, without recourse to look up tables;

2.   The workflow goes like this:
  a.   Compose & focus etc without any filters;
  b.   Put on the ND1000 and switch to LV (use the ND1000 rather than the ND16 a this stage, unless of course you only need the ND16;
  c.   Set aperture wide open, ie F/4 on my 24-105 and ISO to 100;
  d.   Try Auto-ETTR, but it is likely to fail, sometimes even saying “whoops”;
  e.   Adjust exposure until the ETTR hint reads about 1-3 Ev and exposure is sensible, ie 1-20 seconds usually;
  f.   Take note of the ETTR hint number of stops and adjust according to need, for example the ETTR hint may say 3.1, thus my exposure needs adjusting by 3 stops;
  g.   Adjust aperture as well and as required for time and artist need;
  h.   If I then wish to use my ND16 on top, I will adjust by another 4 stops.

3.   Trying to ‘fool’ the ETTR hint in LV by using ISOs over about 400, fails. As soon as I see a pink spectacled LV I know there is no reliable hint there.

Bottom line: based on my experiments I don’t think the ETTR approach will work for high density ND filters, eg over ND1000, as I fear ML can not reliably get a solution for very long exposures.

So I will keep perfecting the ML-based ETTR-hint approach.

Thanks for the input.

eduperez

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Re: Long Exposure ETTR setting
« Reply #13 on: August 01, 2014, 08:35:33 AM »
Just for your reference, we have a "long exposure calculator" for the 400D (https://code.google.com/p/400plus/wiki/UserGuide#Long_Exposure_Calculator):

The long exposure calculator is a tool created to help the photographer quickly determine the exposure time required by a particular scene. The idea behind the long exposure calculator is that you can quickly measure a scene using a high ISO and a large aperture, then lower the ISO value and reduce the aperture, but increase the exposure time accordingly.

For example, let's suppose we want to photograph a night scene; we decide to use the lowest possible sensitivity (ISO100), to avoid noise, and a relatively closed aperture (f/8), to get the depth of field we need. Using those parameters, the exposure time needed may easily overpass 30 seconds, and thus we cannot use the camera to make a reliable measurement.

But we can temporarily select a high sensitivity and large aperture (ISO1600 and f/2.8, for example), measure the scene, and determine we would need a 15-second exposure with those parameters. Then we enter the long exposure calculator, lower the ISO value to 100, and close the diaphragm to f/8; the Ev indicator will display a value if -9, meaning that with the current parameters the exposure is 9 stops below the measured value. We can now increase the exposition time until the Ev indicator goes back to 0, meaning the current parameters would result in the same exposure than we had at the beginning; in our case, that means raising the exposure time from 15 seconds to 32 minutes. Finally, just press "Apply" to configure the camera with these parameters, and launch the long exposure script.

Notice: The Ev field in this calculator cannot display values smaller than -15EV or larger than +15EV.

Tip: If you plan to use a ND filter, you can measure the scene without the ND; then enter the long exposure calculator and adjust the exposure to get an Ev result inverse to the value of the ND filter. For example, assuming we have an ND8 filter (8 steps of light reduction): if the camera measures 1/120s f/4.0 ISO1600 without the filter, then select 2' f/8.0 ISO100 to achieve a Ev of +8.

garry23

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Re: Long Exposure ETTR setting
« Reply #14 on: August 01, 2014, 03:24:02 PM »
@eduperez

Thanks for the info. If you have a 400D it looks good :-)

I have a 5DIII and a 50D.

Cheers

Garry

dmilligan

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a1ex

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Re: Long Exposure ETTR setting
« Reply #16 on: June 12, 2015, 06:02:09 AM »
I never used ND filters, but this might be also helpful: http://www.magiclantern.fm/forum/index.php?topic=5200.msg149466#msg149466